Orthogonal frequency division multiplexing (OFDM) has been used for Long Term Evolution (LTE) and IEEE 802.11 radio technologies due to its simplicity in mitigating frequency selective channels by converting them into smaller flat fading sub-channels. Discrete Fourier transform spread OFDM (DFT-s-OFDM) may improve the peak-to-average power ratio (PAPR) of OFDM by spreading the data sequence with a DFT before mapping it to sub-carriers at the inverse fast Fourier transform (IFFT) input.
Both OFDM and DFT-s-OFDM may use a cyclic prefix (CP) to prevent the inter-symbol interference (ISI) that may occur due to the channel delay spread and timing synchronization errors. Current LTE systems may support two values of the CP: normal CP and extended CP. The number of OFDM symbols per sub-frame may be 14 for normal CP and 12 for extended CP. As the CP is configured per cell, the system may lose some spectral efficiency if configured for extended CP and not all the wireless transmit/receive units (WTRUs) in the cell may experience the same large delay spread.